Here, we present our recent findings from mapping experiments in field stimulated guinea pig papillary muscle. We monitored the developing local excitation during applied shocks (2.5-10 V/cm, 5 or 10 ms) with very high spatial and temporal resolution. Time maps, based on the occurrence of the maximal upstroke velocities, on exceeding 50% of the signal amplitudes, and on exceeding a presumed excitation threshold of -60 mV were constructed. The local, micro-structure related modulation of the excitation process was gained by subtracting a first-order fit (representing the general tendencies) of these time maps from the original ones. The resulting local time maps show the small, locally appearing temporal deviations related to local tissue discontinuities. In general, structure related modulations were found during the whole excitation phase, even during complex signal developments. In regions with positive shock induced polarizations, with increasing shock strength, the local temporal deviations were diminished; in negatively polarized regions, increased, respectively.